1. Field of Invention
The present invention relates to a method for making a wave-absorbing sheet and, more particularly, to a method for making a thin, light, flexible wave-absorbing sheet that absorbs a wide band of frequency of electromagnetic wave at a high rate.
2. Related Prior Art
A microwave-absorbing material (or “wave-absorbing material”) absorbs electromagnetic wave, transforms the electromagnetic energy into heat, and scatters the heat. Thus, the electromagnetic energy is attenuated.
In the military, wave-absorbing materials are used to conceal weapons from radars or protect radars from electromagnetic interference. In everyday life, wave-absorbing materials are used to protect 3C devices from electromagnetic interference that is getting worse as the frequencies of the pulses of CPUs are getting higher, and high-frequency mobile phones and vehicle-navigating devices are getting more popular.
The foregoing electronic devices produce electromagnetic wave that would interfere with other electronic devices and even hurt human bodies. Hence, there is a need for microwave-absorbing materials that fight undesirable electromagnetic wave (or “electromagnetic noise”). A wave-absorbing material is supposed to effectively absorb electromagnetic wave, transforms the electromagnetic energy into heat, and scatters the heat. Thus, the electromagnetic energy is attenuated. Wave-absorbing materials can be used in microwave anechoic rooms, electromagnetic compatibility, and protection from electromagnetic pollution.
Wave-absorbing materials are used for protecting mobile phones, laptop computers and other 3C from EMI. For example, when an RFID tag or reader/writer is attached to a metal surface, the distance for reading is much shorter than expected. Conventionally, the distance of the RFID antenna from the metal surface is increased to avoid the foregoing problem. The increased distance however renders the RFID tab or reader/writer thick.
Wave-absorbing materials are classified into a magnetic-loss type and an electric-loss type. Wave-absorbing materials are made of iron cores, ferrites, silver/nickel and iron/aluminum/silicon. The metal is grounded into powder and mixed with adhesive for use. The power includes solid particles. The problem with the use of metal is expensive and heavy.
The present invention is therefore intended to obviate or at least alleviate the problems encountered in prior art.